一、 外键字段的增删改查
1.多对多的外键增删改查
图书和作者是多对多,借助于第三张表实现的,如果想绑定图书和作者的关系,本质上就是在操作第三方表
2.如何操作第三张表
问题:让你给图书添加一个作者,他俩的关系可是多对多
多对多的增删该查
1.给图书id=2添加一个作者id=1
book_obj = models.Book.objects.filter(pk=2).first()
print(book_obj.authors)
借助于内置方法add()
book_obj.authors.add(1)
book_obj.authors.add(2,3)
也支持写对象
2.删除
book_obj.authors.remove(1)
3.修改
book_obj.authors.set([1,3])
4.清空表
book_obj.authors.clear()
总结:
操作第三张表 通过外键字段点下面的方法
add remove set clear
二、 多表查询
1.子查询和连表查询
子查询:一个SQL语句的执行结果当成另一个SQL语句的执行条件,分步操作
连表查询:把多个表关联在一起拼接成一个大的虚拟表,然后按照单表查询
inner join
left join
right join
union
select * from course inner join teacher on course.id=teacher_course_id where id=1;
select * from course as c inner join teacher as t on course.id=teacher_course_id left join class on class.id=c.class_id where c.id=1
2.正反向的概念
先判断是正向还是反向查询
1.正向
外键字段在我手上,我查你就是正向查询
2.反向
外键字段在我手上,你查我就是反向查询
3.判断出来正向和反向之后有什么用
正向查询按照字段查询(外键字段)
反向查询按照表名小写或者表名小写_set
3. 子查询
res = models.Book.objects.filter(pk=1).first()
print(res.publish)
print(res.publish.name)
print(res.publish.addr)
book_obj = models.Book.objects.filter(pk=2).first()
print(book_obj)
print(book_obj.authors.all())
print(book_obj.authors.all()[0].name)
print(book_obj.authors.all()[0].age)
author_obj = models.Author.objects.filter(name='jerry').first()
print(author_obj.author_detail)
print(author_obj.author_detail.phone)
publish_obj = models.Publish.objects.filter(name='北京出版社').first()
print(publish_obj.book_set)
print(publish_obj.book_set.all())
print(publish_obj.book_set.all()[0].title)
author_obj = models.Author.objects.filter(name='tom').first()
print(author_obj.book_set)
print(author_obj.book_set.all())
author_detail_obj = models.AuthorDetail.objects.filter(phone=110).first()
print(author_detail_obj.author)
print(author_detail_obj.author.name)
总结:
1. 什么时候加_Set
2. 什么时候.all()
结论:当查询的结果是有多个的时候,就需要以上两个操作
4.多表查询之连表查询(基于双下划线的查询)
'''多表查询之连表查询(基于双下划线的查询)'''
res = models.Author.objects.filter(name='jerry').values('author_detail__phone', 'name')
print(res)
res = models.AuthorDetail.objects.filter(author__name='jerry').values('phone', 'author__name')
print(res)
res = models.Book.objects.filter(pk=1).values('publish__name', 'title')
print(res)
res = models.Publish.objects.filter(book__pk=1).values('name', 'book__title')
print(res)
res = models.Book.objects.filter(pk=1).values('authors__name')
print(res)
res = models.Author.objects.filter(book__pk=1).values('name')
print(res)
res = models.Book.objects.filter(pk=2).values('authors__author_detail__phone')
print(res)
5. 聚合查询(aggregate)
sum max min avg count
select sum(price) from table group by '';
select avg(price) from book;
from django.db.models import Max, Min, Sum, Avg, Count
注意:以后在导模块的时候,只要是跟数据库相关的一般都在
django.db
django.db.models
res = models.Book.objects.aggregate(Max('price'), Min('price'), Sum('price'), Avg('price'), Count('id'))
print(res)
6. 分组查询annotate
1. 使用命令修改
查看sql_mode
show variables like '%mode%';
@@select sql_mode;
set global sql_mode='ONLY_FULL_GROUP_BY'
2. 使用配置文件
res = models.Book.objects.annotate(author_num=Count('authors')).values('author_num', 'title')
print(res)
res = models.Book.objects.annotate(author_num=Count('authors__pk')).filter(author_num__gt=1).values('author_num', 'title','id')
print(res)
res = models.Author.objects.annotate(sum_price=Sum('book__price')).values('sum_price', 'name')
print(res)
7. F查询
'''F查询'''
from django.db.models import F
res = models.Book.objects.filter(maichu__gt=F('kucun')).all()
print(res[0].title)
sql: update book set price = price+500 ;
res = models.Book.objects.update(price=F('price')+500)
from django.db.models.functions import Concat
from django.db.models import Value
res = models.Book.objects.update(title=Concat(F('title'), Value('爆款')))
8. Q 查询
'''Q查询'''
from django.db.models import Q
q = Q()
q.connector = 'or'
q.children.append(("maichu__gt", 600))
q.children.append(("price__lt", 100))
res = models.Book.objects.filter(q)
print(res)
三、django中如何开启事务
原子性
隔离性
持久性
一致性
1.开启事务
start transaction;
2. 提交事务
commit;
3. 回滚事务
rollback;
事务的作用:保证安全,保证多个SQL语句要么同时执行成名, 要么同时失败
'''Django中如何开启事务'''
from django.db import transaction
try:
with transaction.atomic():
...
models.Book.objects.filter(maichu__gt=100, price__lt=600).update()
models.Book.objects.filter(maichu__gt=100, price__lt=600).create()
except Exception as e:
print(e)
transaction.rollback()